Motherwell pulled the plug on David Turnbull’s move to Celtic after Parkhead bosses offered to take the teenager on loan for a year without giving any guarantees they would still buy him next summer, PA understands.

The 19-year-old faces up to six months out after a previously unknown knee problem was unearthed during his Hoops medical.

But Fir Park chiefs were unhappy with the new terms put forward Celtic as they sought to renegotiate their £3.25million deal agreed two weeks ago.

Turnbull’s injury was discovered when the Scotland Under-21 star was sent to Manchester last Friday for a routine MRI scan and he could now miss between three months and the rest of the year after being told he requires urgent surgery.

The ligament problem came as a complete shock to Turnbull, who had no idea there was anything wrong and had suffered no symptoms.

But both Celtic’s specialists and the London experts who Well sought a second opinion from say it is not worth the risk delaying the operation any longer.

The news, though, spooked Celtic into demanding fresh talks on the transfer.

Sources close to the deal say the Parkhead clubs offered to pay a nominal fee to take Turnbull on a 12-month loan, during which they would take over responsibility for rehabilitating the Scottish Football Writers Association’s young player of the year.

If he could then prove his fitness, Celtic said they would go ahead with the deal originally struck on June 12.

The two sides spent Wednesday locked in talks trying to thrash out a way forward.

While Celtic felt their approach was a reasonable compromise given they could simply have walked away from the deal altogether, Motherwell were not satisfied by the fact there was no cast-iron promise to complete the move next summer.

With neither side willing to budge, Motherwell then decided to call the whole thing off.

This fresh twist brings to an end one of the most dramatic transfer chases in recent memory but will be a major blow to Turnbull.

However, Well have vowed to stand by the youngster – who emerged as the hottest talent in Scottish football during a breakthrough campaign last year that saw him score 15 goals in 30 appearances from midfield – and have already booked him in to go under the knife.

The Steelmen released a statement shortly after midday on Thursday which said: “David Turnbull is to remain a Motherwell player, with a proposed move to Celtic FC no longer taking place.

“An agreement was reached with the Glasgow club on 12 June, subject to the player agreeing personal terms, which he did, and undergoing a medical.

“During that medical process, an issue was identified that will require David to have immediate preventative surgery and subsequent rehabilitation.

“Celtic were still keen to sign the player despite this matter arising. But having presented revised transfer terms to Motherwell, the clubs could not reach an agreement.

“David will now remain at Fir Park and will shortly have an operation which will rule him out of any football for an extended period, the exact length to be determined following surgery.

“We will give David all the support he needs during this process. We wish him the best with his procedure and rehabilitation, and look forward to watching him play in claret and amber again in the near future.”

Celtic launched their bid a fortnight ago but then warned Turnbull they were ready to “move on” to other targets after he knocked back their opening “magnificent offer”.

The champions then appeared to have dropped out of the running completely when it was revealed Well had also struck terms with Norwich.

However, Turnbull’s Celtic switch was back on when he decided against a move to Carrow Road following talks with Daniel Farke.

Hoops boss Neil Lennon was even pictured with the player wearing a Celtic kit last Friday but the Parkhead faithful grew anxious as the days ticked by without official confirmation.

Lennon was even quoted on Wednesday night saying he hoped the move was still possible but the Northern Irishman has now been left disappointed.

Celtic reacted to the news with their own statement, saying: “It is unfortunate that we were not able to proceed with the transfer of David to Celtic, having agreed a significant fee with Motherwell and reaching agreement with the player.

“It is regrettable that David will be out of action for a considerable length of time and, clearly, these circumstances are totally out of the club’s control. We did everything we could to find a solution.

“We would like to thank David and his representatives for the professionalism they have shown throughout. We also thank Motherwell FC for the way they have handled this process.

“We wish David all the very best with the operation and every success for the future.”